With ghouls all you really need to do is plop on some balled zombie heads.You could paint them to look a bit more tatty, but the only difference with the game models is that the Ghouls use a different skin (and mesh for the head I think). With my own remnants all I'm doing is that, whilst perhaps adding on some looted gear to replace the soldier's aging equipment. So I'll me equipping them mostly with Chinese gear, but adding on backpacks, extra pouches, shovels, pistols, knives, etc, just to make them a bit more "lived in". Though those models look fine enough as they are just to swap out the heads and use them in your games (if I didn't have my eyes set on the Wargames Factory Russians I may just use them instead).
That's just a West Wind Japanese officer with a simple zombie head swap. =P